1. Technical Field
This invention relates to the field of semiconductor processing. More specifically, the invention relates to recovering semiconductor wafers from a chemical tank.
2. Background Art
In the processing of industrial parts such as semiconductor wafers, automated chemical processing systems are frequently used. In such systems, batches of parts such as semiconductor wafers are immersed in various chemical baths by a robotic handler for very precise, programmed durations. In the event that a malfunction of the robot or associated computer hardware or software occurs, the parts being processed may become xe2x80x9cstrandedxe2x80x9d in the chemical bath and suffer irreparable damage if they can not be removed at the prescribed time. An example of this is in semiconductor manufacturing, where semiconductor wafers are immersed in etchants, such as hydrofluoric acid, to remove part or all of a film, such as a silicon dioxide, silicon nitride, or other type of film. If left in the acid too long, then over etching of the film may occur. Also, undesired etching into underlying films and/or pitting of the underlying silicon wafer may occur. Such circumstances can result in the need to scrap product wafers. The loss of a single batch of semiconductor wafers can represent a cost of many thousands of dollars, and this number increases as batch sizes and wafer sizes increase.
Generally, any recovery of a wafer lot is done manually, although it is not always possible. An operator or maintenance person uses a specially designed, hand-held hook to lift cassettes of wafers from a chemical tank and move them into a rinse tank. Unfortunately, no tool exists which can be used to manually lift the new xe2x80x9creducedxe2x80x9d cassettes currently used in wet tanks to improve flow around wafers. These cassettes are not structurally designed for such lifting and must be lifted by robots which grip both ends of the cassette. Other solutions which have been discussed involve automated or semi-automated backup robots to remove wafer lots if the main robot is disabled. For modern automated processing equipment in the semiconductor industry, manual transfer of stranded wafer lots into a de-ionized water rinse tank, also called a xe2x80x9csafe haven,xe2x80x9d is complicated by modern designs. Modrn wet benches are designed with so-called xe2x80x9cmini-environmentsxe2x80x9d or tool enclosures, robots and associated rails, tank lids and other hardware which are impediments to swift manual access to chemical tanks under emergency conditions. Any effort to remove the wafers from the chemical and transport them into a water tank must be done quickly such that chemical does not evaporate on the wafer surfaces prior to immersion in water. The systems are designed for automated processing without manual intervention and the modern design prevents swift manual intervention.
Furthermore, recent increases in batch sizes (up to 100 wafers per batch currently) and wafer size (up to 300 millimeters (mm) currently) render manual transport of wafer batches ergonomically unfeasible, particulary so considering the nature of the cassettes currently used to hold wafers. As indicated the xe2x80x9creducedxe2x80x9d cassettes have minimal support and are designed to be transported by large robots, not people. Finally, health and safety issues associated with working near hazardous chemicals remain an additional concern. Accordingly, it is undesirable to have fabricator personnel reaching into tanks of hazardous chemicals to remove parts.
Thus, it can be seen from the above discussion that it would be an improvement in the art to provide a method for reducing the damage to industrial parts, such as semiconductor wafers, when a malfunction of a robot or associated computer hardware or software occurs in an automated chemical processing system.
According to the present invention, a method for stopping chemical processing of a semiconductor wafer is provided comprising the steps of: 1) placing a chemical having a water concentration of 92% or less in a tank; 2) processing a semiconductor wafer with the chemical in the tank; 3) quick draining the chemical from the tank; and 4) rinsing the wafer in the tank with a rinsing material to stop chemical action. For example, the rinsing material may be de-ionized water and the rinsing step may include either at least partially filling the tank with water, applying the water with a spray bar, or both. Additionally, depending on the extent of the initial processing, the wafer may be reprocessed after again placing the chemical in the tank.
Another method of chemical processing is provided comprising the steps of: 1) placing a chemical in a process tank; 2) processing a semiconductor wafer with the chemical in the process tank; 3) quick draining the chemical from the process tank into a storage tank; 4) rinsing the wafer in the process tank with a rinsing material to stop chemical action; and 5) recycling the drained chemical from the storage tank to the process tank for use in a subsequent process step.
A method of chemical processing in an emergency is also provided comprising the steps of: 1) placing a chemical in a process tank; 2) processing a semiconductor wafer with the chemical in the process tank; 3) detecting a malfunction in the processing; 4) quick draining the chemical from the process tank; and 5) rinsing the wafer in the process tank with a rinsing material to stop chemical action.
Also, a chemical processing system is provided comprising: 1) a process tank adapted to processing semiconductor wafers in a chemical having a water concentration of 92% or less; 2) a control system adapted to detecting a malfunction in processing; 3) a drain valve adapted to quick draining the chemical in the process tank; 4) a spray bar adapted to applying a rinsing material to the wafers in the process tank; and 5) a recirculation system to recirculate chemical from the process tank through a treatment process.
Another chemical processing system is provided comprising: 1) a process tank adapted to processing semiconductor wafers in a chemical having a water concentration of 92% or less; 2) a control system adapted to detecting a malfunction in processing; 3) a drain valve adapted to quick draining the chemical in the process tank; 4) a storage tank adapted to storing the quick drained chemical; 5) a spray bar adapted to applying a rinsing material to the wafers in the process tank; and 6) a recycling mechanism adapted to returning the quick drained chemical to the process tank.
The foregoing and other features and advantages of the present invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.